This invention relates to a head for a wire dot printer, and more particularly to a head for a wire dot printer wherein a mounting structure for an armature is improved.
FIG. 3 shows an exemplary one of print heads which are used in conventional wire dot printers. The print head shown includes a hollow cylindrical housing 1, and a plurality of movable members located in a circumferential row within the housing 1 and each including a radially extending armature 2 and a wire 3 securely mounted at an end of the armature 2 by a suitable means such as brazing and extending laterally in a printing direction. Each of the armatures 2 is resiliently pressed at an outer end thereof against a yoke core 5 by a respective armature spring 4 interposed between the armature 2 and a ceiling portion of the housing 1 and is thus supported for pivotal motion on the yoke core 5. Each of the armatures 2 is urged upwardly at an inner end thereof toward an annular support projection 7 formed on an inner face of the ceiling portion of the housing 1 by a respective reset spring 6 interposed between the armature 2 and the yoke core 5. Thus, each of the armatures 2 is reciprocally rocked in upward and downward directions around a fulcrum at the outer end thereof by a magnetic force acting in a downward direction in FIG. 3 and a returning force of the reset spring 6. Upon such reciprocal rocking motion of the armatures 2, the wires 3 integrally secured to the armatures 2 are moved axially first in the printing direction and then in the opposite direction to effect printing while they are held in a regular arrangement by an intermediate guide plate 10 and an end guide plate 11 both mounted in a tapering annular housing 9 extending in the printing direction from the housing 1 so that they may provide impact points which generally make two parallel lines.
Referring to FIG. 4, the conventional print head further includes a guide member 12 located between each pair of adjacent ones of the armatures 2 for restraining movement of the adjacent armatures 2 in directions other than the upward and downward directions in FIG. 3. Further, each of the armature 2 has a pair of tabs 13 formed on opposite sides of the outer end thereof and extending in a symmetrical relationship in opposite substantially circumferential directions of the housing 1 while each of the guide members 12 has a receiving portion 14 which has a pair of recesses 14a formed on opposite sides thereof for receiving opposing ones of the tabs 13 of the adjacent pair of armatures 2 therein.
However, with the conventional print head described above, since each of the armatures 2 has a pair of tabs 13 formed thereon, it has a relatively great width in the circumferential direction of the housing 1. Besides, since there is a guide member 12 located between opposing ones of the tabs 13 of an adjacent pair of guide members 12, it is necessary to assure a relatively great distance between a pair of adjacent armatures 2 in the circumferential direction of the housing 1. Accordingly, the conventional print head has a drawback that it has a relatively large size and cannot contribute to reduction in size of a printer.